After David Cameron pledged to make it illegal for him to break his promise not to raise tax if re-elected, Labour has had the pledges engraved into the stone which it has specially commissioned.
The pledge has been met with howls of derision and laughter from his opponents and commentators who called it a "tombstone" and a "pledge cenotaph".
Miliband unveils the stone on the campaign trail
Boris Johnson said it was "absolutely crazy" and a "waste of good stone".
"I think it is absolutely crazy that you've already got the Labour leader commissioning great stones that are going to be engraved like the commandments of Moses or Hammurabi with what he wants to do," he told the BBC's Daily Politics.
"This election is very, very far from a foregone conclusion... The idea of a hung parliament is very far from a foregone conclusion."
Miliband said Cameron and Nick Clegg "eroded trust" by failing to keep to promises on cutting immigration and not raising tuition fees.
Miliband said: : "Nick Clegg and David Cameron have helped erode trust in all political leaders by the way they broke promises on issues like tuition fees and immigration after the last election.
"If I am prime minister I will keep our stone in a place where we can see it every day as a reminder of our duty to keep Labour's promises."
Simon Blackwell, who was one of the writers on the satirical political series The Thick Of It, tweeted:
Scottish Tory leader Ruth Davidson said it "looked stupid" - which is why Better Together decided not to do something similar during the independence referendum campaign.
#EdStone began trending on Twitter, with most people mocking the idea of it.
Meanwhile, the Labour's top Twitter supporter, Dr Eoin Clarke, moved in to defend it.
Another Tweeter compared Miliband to Moses and the tablets.
Labour deputy leader Harriet Harman told Sky News's Murnaghan programme: "We are not talking to other parties, we are talking to the British people and saying `If you vote for us, you will get a cut in tuition fees, you will get a mansion tax which puts more money into the NHS, you will have protection for tax credits'."
Shadow Business Secretary Chuka Umunna told Five Live Pienaar's Politics: "People are going to be faced with a very clear choice on Thursday. Do you vote to cut tuition fees, saving a young person in your family going to university £9,000 over the course of a three year degree, or do you vote for a continuation of young people being given a lorry load of debt if they want to go to university under the Conservatives."
Later today, Cameron is to give a speech appealing to Ukip and Liberal Democrat backers to vote tactically to block a "calamitous" deal between Miliband and the SNP.
He will say: "If you have a view about who you would prefer as a Prime Minister, express it at the ballot box - the outcome won't be decided in any other way."